Prior to the development of the petroleum industry in the first part of the latter half of the 1800's, coal and oil shale had been used as primary sources of energy. However, with the discovery of sources of crude oil and the development of the petroleum industry, the use of coal and oil shale as a source of energy markedly declined.
However, in the mid-1970's as a result of political and economic factors increasing the world oil price markedly and with the recognition that at some time in the future liquid petroleum reserves would be exhausted, the energy industry turned to alternative sources of fossil fuel. Activities in research and development of shale oil and coal thereby increased substantially. This research and development activity has predominantly been directed toward producing readily available supplies of energy from not oil shale and coal but also to recover oil locked up in tar sands such as those in the well-known Athabasca tar sand deposits in Canada.
The world supply of oil shale, coal and tar sands is markedly larger than presently known world reserves of liquid petroleum. Procedures to unlock the components of oil shale, coal and tar sands to substitute for present petroleum products produced from crude oil have been actively investigated by many large oil companies. Generally, the approach has been to resort to retorting processes to recover the components locked up in oil shale, notably kerogen, coal and tar sands.
Unfortunately, the level of oxygen-, nitrogen- and sulfur-containing components in oil recovered from oil shale, coal and tar sands is typically much higher than that experienced with petroleum. Industrial concerns exist as to the presence of sulfur and nitrogen impurities in oil derived from such sources because their presence can lead to corrosion of processing equipment, and poisoning of catalysts used in cracking or reforming of the oil in producing various desirable consumer products therefrom. This has meant that in addition to research and development on efficient and economically viable methods of not only recovering the oil from oil shale, coal and tar sand sources, methods to remove or at least reduce the level of these impurities are essential.
Further, with increasing environmental concerns and with more stringent federal, state and local regulations on emission of noxious gases into the environment, for this reason along research and development on methods of reduction of such impurities are essential.
The problem of removal of particularly sulfur and nitrogen compound impurities from oil sources such as shale oil has been recognized in the art. The most generally used present approach for desulfurizing petroleum is catalytic hydro-desulfurization at high temperature and high pressure. In this process, hydrogen is reacted with the sulfur present as an impurity to form hydrogen sulfide and the hydrogen also reacts with the nitrogen present in the impurities to form ammonia. The hydrogen sulfide can be scrubbed and ammonia is removed generally with water washing. Unfortunately, the hydro-desulfurization process for purification involves a high operating cost because of the high temperature and high pressure conditions of operation, the necessity for use of safety precautions when hydrogen is employed, the consumption of hydrogen which is expensive, undesirable hydrogenation of unsaturated hydrocarbons present in the oil and catalyst usage, to name a few of the problems recognized with catalytic hydro-desulfurization of oil obtained from sources such as oil shale, coal and tar sands.
Recently, with the change in economic conditions resulting in a marked decrease in world oil prices and a surplus of oil available from conventional petroleum sources, research and development toward production of alternative energy sources from oil shale, coal and tar sands have become more difficult to justify economically. However, it must be recognized that employing oil shale, coal and tar sands as energy sources will ultimately become a necessity to supply the world's energy needs. Thus, it is particularly important to develop methods of removal of impurities, particularly sulfur- and nitrogen-containing organic compounds from oil produced from oil shale, coal and tar sands.
The invention described and claimed herein is directed to a process for sulfur- and nitrogen-containing organic compound impurity removal from hydrocabonaceous oils utilizing an oxidation/extraction/separation approach to impurity removal in opposition to the currently used catalytic hydro-desulfurization approach as conventionally practiced.
As to the oxidation of petroleum stocks to remove sulfur-containing compounds, oxidation using nitric acids was investigated as early as 1893 (as disclosed in U.S. Pat. No. 508,479) and a process is described in U.S. Pat. No. 542,849, issued in 1895, which involves the oxidation of petroleum stocks using nitrous acid fumes. Further, U.S. Pat. No. 1,864,541, issued in 1925, discloses the oxidation of organic compounds by nitrogen oxides at 400.degree. to 500.degree. C. with contact times on the order of seconds, the oxidation being either homogeneous or catalytic using copper and silver catalysts. U.S. Pat. No. 1,933,748 describes the utilization of nitrogen oxides to remove sulfur compounds from cracked petroleum stocks at 150.degree. to 350.degree. F. followed by the use of sulfuric acid for extraction and U.S. Pat. No. 1,935,207 describes a similar process with disclosure of improved results where the oxidation is carried out using nitrogen oxides in the presence of sulfuric acid at a temperature below 30.degree. C. U.S. Pat. No. 2,009,898 describes the treatment of cracked gasoline vapors with nitrogen oxides without significant olefin oxidation, followed by clay-treatment of the product to achieve a reduction in sulfur content. U.S. Pat. No. 2,825,744 discloses a similar process operated in the vapor phase at temperatures less than 200.degree. C. to produce low molecular weight sulfoxides.
Techniques, including an extraction step, for removal of sulfur impurities from oil are also known. For example, U.S. Pat. No. 2,114,852 discloses a process comprising heating high boiling hydrocarbon oils or shale containing objectionable sulfur compounds as an impurity to obtain hydrocarbon fractions, extracting the product obtained with polar solvents to remove high boiling sulfur compounds in the presence of unsaturated hydrocarbons, followed by oxidizing the extract. U.S. Pat. No. 3,163,593 describes a process using a number of different types of oxidants, including nitrogen dioxides, to treat vacuum residues, residues from cracking processes, oil from tar sands and oil shale followed by thermal decomposition at 350.degree. to 400.degree. C. to produce volatile sulfur compounds and low sulfur oil. The disclosure in this patent is that an alkaline material such as dolomite or lime can be used to accelerate the process.
The use of air as an oxidizing agent for thermally decomposed residues, along with Group 5A and Group 8 metal catalysts, as an alternative to nitrogen oxides, followed by hydro-desulfurization is disclosed in U.S. Pat. No. 3,341,448. A disclosed advantage of this procedure is higher degrees of desulfurization at comparable conditions than can be achieved with hydro-treating alone.
Oxidation/extraction processes of hydrocarbonaceous oils to produce sulfoxides and sulfones are also known in the art as disclosed in U.S. Pat. No. 2,825,744, British Pat. No. 442,524, U.S. Pat. No. 2,702,824, and U.S. Pat. No. 2,925,442.
The art also recognizes that nitrogen removal from oil can be also achieved by oxidation. For example, U.S. Pat. No. 3,105,812 discloses the treatment of a variety of petroleum stocks or shale oil with air or ozone utilizing mixed phosphorus and vanadium oxide catalysts. The disclosure is that preoxidation appears to remove those nitrogen-containing compounds which are more difficult to remove by hydrogenation and as a result, any subsequent hydrodenitrification step can be conducted under less severe conditions for complete nitrogen removal than if a hydrodenitrification step were used alone.
Further, U.S. Pat. Nos. 3,847,800 and 3,919,402 describe the use of nitrogen oxides followed by extraction by methanol to remove both sulfur and nitrogen compounds from petroleum stocks.
It is known in the art that liquid extraction can be employed to separate oxidized sulfur compounds and nitrogen compounds from oil. A hydrolysis reaction with a dilute base to separate the inorganic compounds from a hydrocarbon is described in U.S. Pat. No. 3,847,800. Separations in the organic chemistry field to remove sulfur and nitrogen impurities utilize physical interactions between sulfur and nitrogen compounds as a solute in a solution and the solvents employed for extraction, with an advantageous physical difference being polarity. Since oxidized organic compounds are generally polar in nature, based on these physical principles, this might suggest a successful solvent for extraction, for example, of impurities from a hydrocarbonaceous oil would be a polar solvent. Further knowledge of solvent extraction procedures would indicate that a solvent for use in extraction of impurities from a hydrocarbonaceous oil desirably would be of immiscibile in the oil, would not form an emulsion with the oil, would have a different density from the oil and would have a boiling point difference to facilitate recovery of solvent after the extraction. From a commercial standpoint, advantageously the solvent should also be low in cost and should not alter, in the case of hydrocarbonaceous oils, the ability of such to be subsequently used as a fuel.
As described above, methanol is disclosed in U.S. Pat. Nos. 3,847,800 and 3,919,402 as a solvent to remove both sulfur and nitrogen compounds after oxidation of petroleum stocks using nitrogen oxides. U.S. Pat. No. 2,114,852 discloses a preference for solvents whose boiling points are no more than 80.degree. C. below the boiling range of the initial hydrocarbonaceous oil mixture to facilitate ease of fractionation. I. N. Diyarov, Khim. Tekhnol. Topl. Masel, (5), p. 14-16 (1978) discloses treatment of diesel fuel with ethylene chlorohydrin mixed with water and Yu. E. Nikitin, Neftekhimiya, 16, (6), p. 917-920 (1976) describes a comparison of extraction of sulfoxides from diesel fuel using citric and tartaric acids with citric acid being found to be five times more efficient than tartaric acid in the extraction of sulfoxides. An aqueous solution of quaternary ammonium compounds (as disclosed in Japanese Patent Application (OPI) No. 74-30,401) and an aqueous alkali and organic solvents (as disclosed in U.S. Pat. No. 3,164,546) are also described in the art as suitable for treating diesel fuel oil. Further, U.S. Pat. No. 4,113,607 describes the use of ferric chloride and furfural as an effective solvent in reducing the nitrogen content in hydrogenated oils and U.S. Pat. No. 3,804,749 discloses the utilization of a complex of boron trifluoride in a petroleum immiscible solvent to remove sulfur in oil.
Knowledge of hydrocarbonaceous oils produced from sources such as oil shale, coal and tar sands indicates that a major component of the sulfur compounds in oil from these sources is thiophenic sulfur. As a result, processing to remove impurities from hydrocarbonaceous oils, particularly where sulfur-containing impurities are present, should involve a recognition that thiophenic sulfur-containing compounds must be removed and, based on the art, this would appear to be difficult without sufficient oxidation of the crude hydrocarbonaceous oil.
Approaches toward oxidation of sulfur impurities such as thiophenic compounds to sulfoxides and sulfones and to correspondingly achieve an oxidized form of the organic nitrogen compound impurities present to convert such impurities into forms more easily extractable without loss of the desirable hydrocarbonaceous oil or alteration thereof has, in the past, met with some limited success.
Unfortunately, the prior art approaches toward oxidation to remove a portion of the original sulfur content as gaseous sulfur oxides and to convert a portion of the original sulfur content into sulfoxides and/or sulfones followed by extraction with appropriate solvents to achieve a desired low sulfur raffinate have not been completely successful.
The prior art methods described above basically have the disadvantages that (a) they are sufficiently nonselective that extremely severe oxidizing conditions are required to effect sulfur removal, resulting in undesirable and substantial increases in the nitrogen content of the oil; (b) they use a solvent which is suitable only for specific selected oils, they result in poor extraction yields or they do not result in sufficient phase separation that solvent extraction is possible; (c) they require expensive or complicated processing equipment; or (d) they involve combinations of the disadvantages enumerated above.
Thus, present technology for impuritiy removal involving oxidation and subsequent extraction of hydrocarbonaceous oils needs to be greatly improved. Similarly, direct extraction of hydrocarbonaceous oils with selected solvents to remove sulfur and nitrogen impurities to produce a raffinate which is low in sulfur and nitrogen content results in uneconomically low yields of the desired raffinate, reductions in the sulfur and nitrogen content of the hydrocarbonaceous oil which are uneconomic or combinations of these. The prior approaches involving high temperature, high pressure hydro-desulfurization to reduce the sulfur and nitrogen content of hydrocarbonaceous oils involve a number of major disadvantages. As indicated previously, the high temperature, high pressure requirements of the process makes the process quite expensive. The hydrogen required in the process is expensive and requires water for its production. Unfortunately, in those areas where major deposits of oil shale exist, water to produce the hydrogen may well be in short supply. Investigations of the process have resulted in finding that the process is nonselective in that although sulfur and nitrogen compounds are removed, desirable olefinic or aromatic compounds are also destroyed. Processing of the products produced such as hydrogen sulfide, which is highly toxic, and ammonia also contributes to the expense of the process and in view of the catalytic nature of the process, with the catalyst being poisoned by materials contained in the hydrocarbonaceous oil, this even further contributes to the expense of the process. All of these factors result in the process not being economically desivable.